In many industrial, military, security or medical applications, images of an internal structure of objects are required. Radiography is one type of technique that can be used for imaging. Radiography generally comprises either conventional transmission radiography or backscatter radiography. When access behind an object to be interrogated is not possible, only backscatter radiography is possible. One method of backscatter imaging is Compton Backscatter Imaging (CBI), which is based on Compton scattering.
Lateral migration radiography (LMR) is one type of imaging based on CBI that utilizes both multiple-scatter and single-scatter photons. LMR uses two pairs of detector with each pair having a detector that is uncollimated to predominantly image single-scatter photons and the other detector collimated to image predominantly multiple-scattered photons. This allows generation of two separate images, one containing primarily surface features and the other containing primarily subsurface features.
Recently, backscatter radiography by selective detection (RSD), a variant of LMR, has been used. RSD uses a combination of single-scatter and multiple-scatter photons from a projected area below a collimation plane to generate an image. As a result, the image has a combination of first-scatter and multiple-scatter components, offering an improved subsurface resolution of the image.